1. Field of the Invention
The present invention relates to rotary actuators of the type which utilize pressurized fluid to produce rotary motion, and more particularly relates to a novel and improved actuator which is well adapted for use with a variety of valves requiring a stem rotation of about 90.degree..
2. Prior Art
A number of fluid operated rotary actuators have been proposed which typically include a reciprocable piston coupled to a rotatable stem for rotating the stem as the piston is reciprocated. Most of these proposals provide a relatively compex and expensive actuator assembly, particularly where the actuator has a relatively high torque output rating.
There has been a need for a relatively simple and inexpensive actuator for use with valves which require a stem rotation of about 90.degree.. One problem presented by such applications is a wide variance in valve stem configurations. Present day valve stems have end configurations which typically include opposed flats, squares of various sizes, splines, and other shapes. Providing a reliable and readily adaptable actuator-to-valve stem connection is a significant concern.
Another problem encountered in providing a versatile valve actuator is the need for a compactly constructed actuator capable of relatively high-torque outputs near the ends of its rotational stroke. Many valve installations are made in closely confined areas which necessitate a compact actuator structure. Many valves additionally require the application of relatively high torque forces in seating and unseating the valves, but need only low torque forces at other times. Most known actuators have not satisfied the need for a compactly constructed device capable of producing a high torque for seating and unseating valves.
Still another problem is that many valves are installed in submerged locations. A number of present day actuators are not well adapted for submerged installation.
Still another problem with many proposed doubleacting rotary actuators is that their assembly is complicated by a need to interconnect a lever with an actuator piston after the piston has been inserted in the housing. Prior art proposals have not permitted the assembly of a piston and lever while the piston is removed from the housing because once the piston and lever are assembled, the piston cannot then be inserted into the housing.
Some prior art proposals describe an actuator having a housing which reciprocally mounts a piston, which journals an output shaft, and which houses a lever that interconnects the piston and the output shaft. Most of these proposals rigidly connect the lever to the rotating stem and slidably connect the lever to the piston. Such proposals provide a sliding thrust connection with the lever which has only a very small, essentially live contact area of surface engagement. This small area of engagement produces a concentration of forces which inhibits efficient operation of the actuator and promotes wear of the parts which form the sliding connection. Forces transmitted longitudinally of the lever cause unnecessary loading of the bearings which journal the stem and inhibit smooth operation of the actuator. Such proposed actuators are not well adapted to carry relatively high loads.
One prior art proposal describes a hydraulic control valve which employs a piston-operated actuator. The actuator has a double ended piston which is normally centered along its stroke by a pair of springs which engage opposite ends of the piston. A slot is formed in a central region of the piston, and one end region of a lever extends into this slot for pinned pivotal connection to the piston. The other end region of the lever is slidably received in a slot formed in a rotatable stem journaled by the actuator housing. The stem is not journaled over a large area of engagement in a region which surrounds its sliding connection with the lever. This relatively light duty actuator is not designed to carry heavy loads but rather is intended simply to position the stem of a hydraulic control. In order to assemble the actuator, the housing is left open along one side to permit access to the pinned pivotal connection between the lever and the piston. The actuator is not well adapted for installation in a submerged application.